X-ray inspection devices are widely used in the fields such as measuring medicine, electronic industry, aerospace industry, etc. In an X-ray inspection device, an inspection function is achieved by such a way that X-rays are converted into visible light, a photodiode receives the light and transforms the photosignal into an electric signal by a photovoltaic effect, and the electric signal is input into a control circuit of the X-ray inspection device with the aid of switching control of a thin film transistor.
For example, a common X-ray detector is an X-ray detector with an amorphous silicon photodiode array as the core, and includes an array substrate; and the array substrate includes a thin film transistor (TFT) and a photodiode. Under the radiation of X-rays, X-ray photos are transformed into visible light by a scintillator layer or a phosphor layer of the detector, next, the visible light is transformed into an electric signal under the action of the photodiode, and the electric signal is read out and output by the thin film transistor. Thus, an image to be displayed is obtained. Storage and readout of the electric signal can be controlled by turning off and turning on the thin film transistor, respectively, so the performance of the thin film transistor is especially important in the device.
Generally speaking, the structure of a thin film transistor mainly includes a substrate, a gate electrode, a source electrode, a drain electrode, a semiconductor layer (an active layer) and a gate insulating layer. Patterns of the gate electrode, the gate insulating layer and the semiconductor layer are successively formed on the substrate, and the source electrode and the drain electrode are formed on the semiconductor layer. In order to avoid poor connection between the source and drain electrodes and the semiconductor layer, caused by inaccurate positioning, such a way of laying the source and drain electrodes to overlap the semiconductor layer is usually adopted.